Reflective liquid crystal display apparatus and production method thereof

ABSTRACT

The present invention provides a reflective liquid crystal display (LCD) apparatus including a glass substrate  53 , a transparent electrode  55  arranged on the glass substrate, a glass substrate  40 , a thin film transistor (TFT)  44  arranged on the glass substrate  40 , an insulation film  45  arranged on the TFT  44  and having a convex/concave structure  45   a  on its surface, a reflection electrode  48  arranged along the convex/concave structure  45   a  and connected to the TFT  44 , and a liquid crystal layer  56  sandwiched between the transparent electrode  55  and the reflection electrode  48 . The insulation film  48  protects the TFT transistor  44  after being formed and has the convex/concave structure  45   a  formed irregular arrangement of regions having different film thickness values. Thus, it is possible to prevent deterioration of the switching element during the production as well as to reduce the number of production steps.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflective liquid crystal display(LCD) apparatus having a reflection plate for reflecting to outside alight which has passed through a liquid crystal layer from outside.

2. Description of the Related Art

As compared to a transmitting LCD apparatus, a reflective LCD apparatuscan reach a reduced power consumption and a thin type with a reducedweight and accordingly, has been used mainly in a portable terminal. Inthe reflective LCD apparatus, light incident from outside is reflectedby a reflection plate in the apparatus so as to be utilized as a displaylight source, thereby eliminating need of back light.

The conventional reflective LCD apparatus has a basic configurationcomposed of a liquid crystal of the TN (twisted nematic) type, a singledeflection plate type, STN (super twisted nematic) type, GH (guest-host)type, PDLC (high molecule dispersion) type, or cholesteric type, aswitching element for driving the liquid crystal, and a reflection platearranged inside or outside liquid crystal cells. The reflective LCDapparatus utilizes an active matrix drive method capable of realizing ahigh-resolution and high-quality image by using a thin film transistor(TFT) or metal/insulation film/metal structured diode (MIM) as aswitching element, to which a reflection plate is attached.

FIG. 36 is a cross sectional view of a conventional reflective LCDapparatus of a single deflection plate type. Hereinafter, explanationwill be given with reference to this figure.

An opposing substrate 1 includes a deflection plate, a phase differenceplate 32, a glass substrate 4, a color filter 5, and a transparentelectrode 6. A lower substrate 7 includes a glass substrate 8, a thinfilm transistor (TFT) 9 of an inverse stagger structure as a switchingelement formed on the glass substrate 8, an insulator protrusion 10 as abase for forming a, a polyimide film 11 as an inter-layer insulationfilm formed thereon, and a reflection electrode 13 connected to a sourceelectrode 12 of the TFT and functioning as a reflection plate and apixel electrode. A liquid crystal layer 14 is arranged between theopposing substrate 1 and the lower substrate 7.

A reflected light 16 is utilized as a light source. An incident light 15from outside passes through the deflection plate 2, the phase differenceplate 3, the glass substrate 4, the color filter 5, the transparentelectrode 6, and the liquid crystal layer 14, and is reflected by thereflection electrode 13 to become the reflected light 16.

This reflective LCD display apparatus should have a display performancefor displaying a bright and white display when the liquid crystal is inthe light transmitting state. In order to realize this displayperformance, it is necessary to effectively eject forward the incidentlight 15 from various directions. For this, the polyimide film 11 isformed with the convex/concave structure, so that the reflectionelectrode arranged thereon can have a scattering function. Accordingly,control of the convex/concave structure of the reflection electrode 13is the important factor in deciding the display performance ofthe/reflective LCD apparatus.

FIG. 37 and FIG. 38 show a production method of a conventionalreflective LCD apparatus in cross sectional views. Hereinafter,explanation will be given with reference to these figures.

In the thin film transistor production procedure, firstly, a gateelectrode 21 is formed on the glass substrate 20 (FIG. 37[a]). Next, agate insulation film 22, a semiconductor layer 23, a doping layer 24 areformed (FIG. 37[b]). Next, an island 25 of the semiconductor layer 23and the doping layer 24 is formed (FIG. 37[c]), and the source electrode26 and the drawing electrode 27 are formed (FIG. 37[d]). After this, thereflection electrode is formed.

For forming the reflection electrode, firstly, an organic insulationfilm 28 having photosensitivity is formed (FIG. 37[e]). Then,photolithography is performed to form a protrusion 29 in the reflectionelectrode forming region (FIG. 37[f]), which is then melted by heatingso as to be formed into a smooth protrusion 30 (FIG. 38[g]). Next, theprotrusion is covered by an organic insulation film 31 to obtain afurther smooth convex/concave surface 32 (FIG. 38[h]). Next, a contactportion 33 is formed for electrically connecting a reflection electrodeto a source electrode of the thin film transistor (FIG. 38[i]), and thenthe reflection electrode 34 is formed (FIG. 38[j]). The method forforming this reflection electrode is disclosed, for example, in JapanesePatent Publication (examined) 61-6390 or in Tohru Koizumi and TatsuoUchida, Proceeding of the SID, Vol. 29, 157, 1988.

As has been described above, in the conventional reflective LCDapparatus, the convex/concave structure is formed by organic insulationfilm or inorganic insulation film having photosensitivity as a basewhich is covered by an organic insulation film or inorganic insulationfilm.

However, below the protrusions, there are formed a metal wiring, anelectrode, a switching element, and the like, which are exposed to anetching liquid used in the etching procedure for forming theprotrusions. As a result, a reaction between the etching liquid and theundercoat film deteriorates characteristic of the switching element andthe remaining etching liquid lowers reliability of the switchingelement.

Moreover, when using an organic insulation film or inorganic insulationfilm having no photosensitivity for the insulation film below thereflection electrode, a photo resist pattern is formed on the insulationfilm and dry etching is performed to form a convex pattern. In thiscase, the undercoat film is exposed to plasma during the etching and theplasma damage deteriorates the characteristic of the switching element.

On the other hand, the conventional method for producing theconventional reflective LCD apparatus requires a number of productionsteps as has been described above. This increases the production cost,which in turn increases the cost of a reflective LCD apparatus. Thereason why the reflective LCD apparatus requires a number of productionsteps is that a high-performance switching element and ahigh-performance reflection plate are formed on the same insulationsubstrate in order to obtain a bright high-quality display, and that theproduction of the high-performance reflection plate requires a methodcapable of forming the convex/concave structure on the reflection platesurface with a desired configuration. Accordingly, the conventionalreflective LCD apparatus requires a number of film formation steps,photoresist (PR) steps, and etching steps.

Currently, no effective means is employed to simplify the productionprocedure. The convex/concave structure below the reflection electrodeis currently produced as follows. Firstly, a photosensitive resin isapplied, which is then patterned by an exposure step and a developmentstep so as to form a convex pattern. However, in the area other than theportion having this convex pattern, the photosensitive resin film iscompletely removed. After this, the convex pattern is subjected to athermal treatment so as to obtain a smooth protrusion shape, which isthen covered by an organic insulation layer so as to obtain a desiredsmooth convex/concave surface.

That is, the insulation film below the reflection electrode consists oftwo layers: a film of convex shape and a film covering it. Thisinsulation film has a function as an inter-layer insulation film forelectrically insulating the reflection electrode from the switchingelement and the wiring. After this, a contact hole is formed in thisinsulation layer. Then, a metal thin film such as aluminum is layeredthereon. This metal thin film is patterned to obtain a reflectionelectrode along the fine convex/concave structure of the insulationfilm.

Thus, formation of the reflection electrode has required five steps: (1)formation of an insulation film for forming a protrusion as a base; (2)formation of a protrusion; (3) formation of a contact hole; (4)formation of a metal thin film having a high reflection efficiency; and(5) formation of a reflection electrode.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide areflective LCD apparatus and a production method thereof for enabling ahigh-luminance and high-quality display capability by preventingdeterioration of the switching element in the production procedure aswell as reducing the production cost by reducing the number ofproduction steps.

The reflective liquid crystal display (LCD) apparatus according to thepresent invention includes: a transparent first substrate; a transparentelectrode arranged on the first substrate; a second substrate; aswitching element arranged on the second substrate; an insulation filmarranged on the switching element and having a convex/concave structure;a reflection electrode arranged on the insulation film along theconvex/concave structure and connected to the switching element; and aliquid crystal layer sandwiched between transparent electrode of thefirst substrate and the reflection electrode of the second substrate.The insulation film protects the switching element after formed and theconvex/concave structure is formed by irregular arrangement of regionshaving different thickness values.

In a conventional reflective LCD apparatus, protrusions are located on ametal wiring, electrode, switching element, and the like, which areexposed to a process atmosphere when forming the protrusions, causingdeterioration of the switching element. According to the presentinvention, since the insulation film always covers the metal wiring, theelectrode, the switching element, and the like, they are not exposed toa process atmosphere can be protected from a process damage. Moreover,in the present invention, the insulation film has regions havingdifferent film thickness values, i.e., protrusions having a large filmthickness and indentations having a small film thickness. Thiseliminates need to form another film for the convex/concave structure.

According to another aspect of the present invention, the convex/concavestructure has a continuous smooth shape. This enables to obtain a brightdisplay because the luminance of the reflective LCD apparatus isdetermined by the inclination angle of the convex/concave structure ofthe reflection electrode.

According to yet another aspect of the present invention, the insulationfilm may be a single-layered film made from a single material. Thus, theinsulation film is formed by a single layer by a single step. That is,there is no need to form the convex/concave structure and theinter-layer insulation portion by separate steps. This simplifies theconvex/concave structure formation step which is complicated in theconventional reflective LCD apparatus.

According to still another aspect of the present invention, theinsulation film may have a light absorption characteristic. Thus, theinsulation film can absorb an incident light from between adjacentreflection electrodes. This enables to shut out the incident light whichmay be introduced to the back side of the reflection electrode, therebysuppressing radiation of the incident light to the switching element andenabling to realize a preferable switching characteristic.

According to still yet another aspect of the present invention, theconvex/concave structure may have a plurality of protrusions arrangedirregularly. This can suppress interference of the reflected light fromthe reflection electrode, thereby enabling to form a convex/concavestructure having a preferable reflection capability. Furthermore, theprotrusions may have an island shape or a line shape in a plan view.This enables to obtain a bright reflection capability. That is, in thereflective LCD apparatus using such a convex/concave structure, it ispossible to obtain a bright display characteristic.

Moreover, the convex/concave structure may have a plurality ofindentations arranged irregularly. This suppresses interference of thereflected light from the reflection electrode, thereby enabling to forma convex/concave structure having a preferable reflectioncharacteristic. Furthermore, the indentations may have a hole shape or aline shape in a plan view. This enables to obtain a bright displaycharacteristic. That is, in the reflective LCD apparatus using such aconvex/concave structure, it is possible to obtain a bright displaycharacteristic.

Moreover, the convex/concave structure may be formed by repetition of anirregular convex/concave shape based on one or more than one pixels.This can suppress interference of the reflected light. Accordingly, thereflective LCD apparatus produced by using this reflection electrode hasno wavelength dependency by the light source or no deterioration of thecolor characteristic, thereby enabling to obtain a bright high-qualitydisplay characteristic.

Moreover, the insulation film having the convex/concave structure may bemade from an organic resin or inorganic resin having photosensitivity.In this case, it is possible to form a desired convex/concave pattern byperforming exposure and development directly to the photosensitiveresin, eliminating the need of photoresist application, formation,development, and peel-off steps. Thus, the number of production steps isreduced, thereby enabling to reduce the cost of the reflective LCDapparatus.

The present invention also provides a reflective LCD apparatusproduction method for producing the reflective LCD apparatus. That is,the convex/concave structure is formed by performing photolithography tothe insulation film to form a predetermined pattern while leaving apredetermined film thickness, so as to form regions having a large filmthickness and regions having a small film thickness arranged irregularlyin a plan view.

Thus, the convex/concave structure is formed in the insulation filmusing a mask pattern, which enables to accurately control a plan shapeof the convex/concave pattern and to form a desired convex/concavepattern with a high reproducibility. Furthermore, when the insulationfilm is etched leaving a desired film thickness, it is possible tocontrol the cross sectional shape of the convex/concave pattern with ahigh reproducibility. Accordingly, it is possible to realize apreferable convex/concave structure. Moreover, this can be performed bya single photoresist step and a single etching step. This cansignificantly simplify the production procedure. Moreover, since themetal wiring, the electrode, the switching element, the insulation filmare not exposed to the process atmosphere (etching liquid, etching gas,and the like) and are not damaged, thereby enabling to realize areflective LCD apparatus having a preferable element characteristic.

Furthermore, according another aspect of the present invention, theconvex/concave structure may be formed by steps of: forming theinsulation film, photolithography for forming a resist pattern on theinsulation film, etching the insulation film leaving a predeterminedfilm thickness at a lower portion of the insulation film, peeling offthe resist film from the insulation film, and thermal treatment of theetched insulation film to melt the insulation film and make theconvex/concave structure smooth.

According to this production method, it is possible to form aconvex/concave pattern without exposing thee switching element, thewiring, the electrode, and the like located under the insulation film.Accordingly, it is possible to form the convex/concave pattern withoutdamaging the switching element and the like. Moreover, theconvex/concave insulation film under the reflection electrode, unlikethe convex/concave insulation film in the conventional reflective LCDapparatus, does not need a step for forming basic protrusions and a stepfor forming a film thereon. The convex/concave insulation film can beformed by using a single film and by a single step. This simplifies theproduction procedure.

Furthermore, the convex/concave structure may be formed by steps of:forming the insulation layer using an organic insulation material orinorganic insulation material having photosensitivity, performingexposure for forming a convex/concave pattern on the insulation layer,development for performing etching-development so as to leave apredetermined film thickness at a lower portion of the insulation film,and performing thermal treatment of the etched and developed insulationfilm to melt the insulation film and make the convex/concave structuresmooth.

This eliminates the resist application, formation, development, andpeel-off steps required for forming the convex/concave structure.Exposure and development can be performed directly to the photosensitiveresin to obtain a desired convex/concave pattern. Thus, the productionprocedure is further simplified, thereby reducing the cost for producingthe reflective LCD apparatus.

Moreover, it is possible to use an organic insulation material orinorganic insulation material having photosensitivity for the insulationfilm, to which the convex/concave structure and the contact hole aresimultaneously formed by a single development step. This enables to formthe convex/concave structure and the contact hole without using theresist process.

Here, the photosensitivity may be positive type, and the step ofexposure may be performed in such a manner that a smaller exposure lightquantity is applied for formation of the convex/concave pattern and agreater exposure light quantity is applied for formation of the contacthole pattern. This eliminates the contact formation step, therebysimplifying the production procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a reflective liquid crystal display(LCD) apparatus according to Embodiment A1 of the present invention.

FIG. 2 shows a reflective LCD apparatus production method according toEmbodiment B1 of the present invention in cross sectional views FIG.2[a] to FIG. 2[e] performed in this order.

FIG. 3 shows a reflective LCD apparatus production method according toEmbodiment B2 of the present invention in cross sectional views FIG.3[a] to FIG. 3[c] performed in this order.

FIG. 4 shows the reflective LCD apparatus production method according toEmbodiment B2 of the present invention in cross sectional views FIG.4[d] to FIG. 4[f] performed in this order.

FIG. 5 shows a reflective LCD apparatus production method according toEmbodiment B3 of the present invention in cross sectional views FIG.5[a] to FIG. 5[e] performed in this order.

FIG. 6 shows a reflective LCD apparatus according to Embodiment A2 ofthe present invention in a cross sectional view.

FIG. 7 shows a reflective LCD apparatus according to Embodiment A3 ofthe present invention in a cross sectional view.

FIG. 8[a] and FIG. 8[b] are plan views showing a first example and asecond example of mask pattern of a reflective LCD apparatus accordingto Embodiment A4 of the present invention.

FIG. 9[a] and FIG. 9[b] are plan views showing a first example and asecond example of mask pattern of a reflective LCD apparatus accordingto Embodiment A5 of the present invention.

FIG. 10[a], FIG. 10[b]. and FIG. 10[c] show a first, a second, and athird example of a reflective LCD apparatus according to Embodiment A6of the present invention.

FIG. 11 shows a comparative example in cross sectional views against areflective LCD apparatus production method according to Embodiment B4 ofthe present invention: steps shown in FIG. 11[a 1] to FIG. 11[f 1] aresuccessively performed in this order.

FIG. 12 shows the reflective LCD apparatus production method accordingto Embodiment B4 of the present invention in cross sectional views:steps shown in FIG. 12[a 2] to FIG. 12[c 2] are successively performedin this order.

FIG. 13[a] shows a first example and FIG. 13[b] shows a second exampleof a reflective LCD apparatus according to Embodiment A7 of the presentinvention in cross sectional views.

FIG. 14 shows a reflective LCD apparatus production method according toEmbodiment B5 of the present invention in cross sectional views: stepsshown in FIG. 14[a] to FIG. 14[g] are successively performed in thisorder.

FIG. 15 shows the reflective LCD apparatus production method accordingto Embodiment B5 of the present invention in cross sectional views:steps shown in FIG. 15[h] to FIG. 15[k] are successively performed inthis order.

FIG. 16 shows a reflective LCD apparatus production method according toEmbodiment B6 of the present invention in cross sectional views: stepsshown in FIG. 16[1] to FIG. 16[3] are successively performed in thisorder.

FIG. 17 shows the reflective LCD apparatus production method accordingto Embodiment B6 of the present invention in cross sectional views:steps shown in FIG. 17[4] to FIG. 17[6] are successively performed inthis order.

FIG. 18 shows a reflective LCD apparatus production method according toEmbodiment B7 of the present invention in cross sectional views: stepsshown in FIG. 18[a] to FIG. 18[g] are successively performed in thisorder.

FIG. 19 shows the reflective LCD apparatus production method accordingto Embodiment B7 of the present invention in cross sectional views:steps shown in FIG. 19[h] to FIG. 19[k] are successively performed inthis order.

FIG. 20 shows a reflective LCD apparatus production method according toEmbodiment B8 of the present invention in cross sectional views: stepsshown in FIG. 20[a] to FIG. 20[h] are successively performed in thisorder.

FIG. 21 shows the reflective LCD apparatus production method accordingto Embodiment B8 of the present invention in cross sectional views:steps shown in FIG. 21[i] to FIG. 21[j] are successively performed inthis order.

FIG. 22 shows Example 1 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 22[a] to FIG. 22[f] are successively performed inthis order.

FIG. 23 shows Example 1 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 23[g] to FIG. 23[j] are successively performed inthis order.

FIG. 24 is a cross sectional view of a reflective LCD apparatus preparedby Example 1 of the present invention.

FIG. 25 shows Example 2 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 25[a] to FIG. 25[g] are successively performed inthis order.

FIG. 26 shows Example 2 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 26[h] to FIG. 26[l] are successively performed inthis order.

FIG. 27 is a cross sectional view of a reflective LCD apparatus preparedby Example 2 of the present invention.

FIG. 28 shows Example 3 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 28[a] to FIG. 28[g] are successively performed inthis order.

FIG. 29 shows Example 2 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 29[h] to FIG. 29[l] are successively performed inthis order.

FIG. 30 shows Example 4 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 30[a] to FIG. 30[g] are successively performed inthis order.

FIG. 31 shows Example 4 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 31[h] to FIG. 31[l] are successively performed inthis order.

FIG. 32 shows Example 5 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 32[a] to FIG. 32[g] are successively performed inthis order.

FIG. 33 shows Example 5 of the reflective LCD apparatus productionmethod according to the present invention in cross sectional views:steps shown in FIG. 33[h] to FIG. 33[l] are successively performed inthis order.

FIG. 34 is a cross sectional view showing Example 5 of the reflectiveLCD apparatus production method according to the present invention.

FIG. 35 is a cross sectional view showing a reflective LCD apparatusaccording to Example 6 of the present invention.

FIG. 36 is a cross sectional view showing a conventional reflective LCDapparatus.

FIG. 37 shows a conventional reflective LCD apparatus productionprocedure in cross sectional views: steps shown in FIG. 37[a] to FIG.37[f] are successively performed in this order.

FIG. 38 shows a conventional reflective LCD apparatus productionprocedure in cross sectional views: steps shown in FIG. 38[g] to FIG.38[j] are successively performed in this order.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a cross sectional view of a reflective liquid crystal display(LCD) apparatus according to Embodiment A1 of the present invention.Hereinafter, explanation will be given with reference to this figure.

The reflective LCD apparatus according to this embodiment includes aglass substrate 53 as a transparent first substrate, a transparentelectrode 55 arranged on the glass substrate 53, a glass substrate 40 asa second substrate, a thin film transistor 44 as a switching elementarranged on the glass substrate 40, an insulation film 45 arranged onthe thin film transistor 44 and having a convex/concave structure 45 aon its surface, a reflection electrode 48 having a shape reflecting theconvex/concave structure 45 a and connected to a source electrode of thethin film transistor 44, and a liquid crystal layer 56 sandwichedbetween the transparent electrode 55 of the glass substrate 53 and thereflection electrode 48 of the glass substrate 40. The insulation film45 is formed with irregular film thickness to form the convex/concavestructure 45 a and protects the thin film transistor 44 after it isformed.

The thin film transistor 44 has an inverse stager configuration composedof a gate electrode, a gate insulation film, a semiconductor film, asource electrode, a drain electrode, and the like formed throughformation of a metal layer 41, an insulation layer 42, a semiconductorlayer 43, and the like, which are then subjected to photolithography andetching. Moreover, on the thin film transistor 44, an insulation layer45 is arranged using an organic insulation material or an inorganicinsulation material. The insulation film 45 has an irregular filmthickness, forming a desired convex/concave structure 45 a which isformed by protrusions 46 having a large film thickness and indentations47 having a small film thickness. On the insulation film 45, areflection electrode 48 is formed. The reflection electrode 48 iselectrically connected via a contact hole 49 through the insulation film45 to a source electrode of the thin film transistor 44 and has also afunction as a pixel electrode.

Moreover, the reflection electrode 48 has a surface reflecting theconvex/concave structure 45 a formed in the insulation film 45 and thisconvex/concave inclination angle determines the optical characteristicof a reflected light. For this, the inclination angle of theconvex/concave structure 45 a is designed so as to obtain a desiredreflection optical characteristic. It should be noted that theconvex/concave structure 45 a need be irregular (with two or morevalues) at least in one of the convex pitch, concave pitch, protrusionheight, and indentation depth.

Next, explanation will be given on the operation of the reflective LCDapparatus according to the present embodiment.

The reflective LCD apparatus operates as follows when in the whitestate. Incident light 50 coming from out of the glass substrate 53passes through the deflection plate 51, the phase difference plate 52,the glass substrate 53, the color filter 54, the transparent electrode55, and the liquid crystal layer 56 and is reflected according to thedirectivity obtained by the convex/concave shape of the surface of thereflection electrode 48. The reflected light again passes through theliquid crystal layer 56, the transparent electrode 55, the color filter54, the glass substrate 53, the phase difference plate 52, and thedeflection plate 51 before returning outside as a display light 58. Onthe other hand, the reflective LCD apparatus in the black state operatesas follows. The incident light 50 passes through the deflection plate51, the phase difference plate 52, the glass substrate 53, the colorfilter 54, the transparent electrode 55, and the liquid crystal layer56, and is reflected by the reflection electrode 48. However, thereflected light is stopped by the deflection plate 51 and cannot gooutside. Thus, the light ON/OFF operation is performed.

FIG. 2 shows a reflective LCD apparatus production method according toEmbodiment B1 of the present invention in cross sectional views.Hereinafter, explanation will be given with reference to this figure.

Firstly, a thin film transistor 44 is formed on a glass substrate 40(FIG. 2[a]). Next, an acrylic resin film 60 is formed as an organicinsulation film. A photoresist (not depicted) is applied thereon, whichis exposed to light to form a convex/concave pattern. Etching isperformed to form a convex/concave pattern 61 in the acrylic resin film60. After this, the photoresist is peeled off (FIGS. 2[b] and [c]).Next, photoresist (not depicted) is again applied, exposed, anddeveloped. The acrylic resin film 60 is etched, the photoresist ispeeled off, and a contact hole 62 is formed in the acrylic resin film 60(FIG. 2[d]). Lastly, an aluminum film is formed, photoresist is applied,exposed, and developed. The aluminum film is etched and the photoresistis peeled off, thereby forming a reflection electrode 63 (FIG. 2[e]).

In the formation of the convex/concave structure in the acrylic resinfilm in steps shown in FIGS. 2[b] and [c], a protrusion 46 having alarge film thickness and an indentation 47 having a small film thicknessare formed. By leaving the acrylic resin film 60 even in the regionhaving a small film thickness, the switching element 44 can be entirelycovered by the acrylic resin film 60. Here, the acrylic resin film 60under the resist pattern is etched to a desired depth so as to leave athin acrylic resin film 60. Thus, it is possible to form aconvex/concave structure which also serves as an inter-layer insulationfilm by the same material and the same process. It should be noted thatby controlling the etching amount, it is possible to adjust the height64 of the protrusion 46 and the film thickness of the indentation 47.Accordingly, it is possible to adjust the convex/concave structure orthe film thickness of the indentation.

It should be noted that acrylic resin is used in this embodiment for theinsulation film but the insulation film can be formed by using anymaterial which simultaneously satisfies the convex/concave heightrequired for the reflection plate optical characteristic and the filmthickness required as the inter-layer film. For example, it is possibleto use a polyimide resin or other organic resins. Moreover, it is alsopossible to use an inorganic insulation film such as a silicon nitridefilm and a silicon oxide film.

Here, considering the directivity of the reflected light, theconvex/concave structure preferably has a height in a range from −0.2 to4 micrometers and a pitch in a range from 1 to 30 micrometers.Furthermore, protrusions and indentations are to be arranged irregularlyon a surface. That is, the protrusions may be arranged in anisland-shaped pattern or a line-shaped pattern and the indentations maybe arranged in a hold-shaped patter or a groove-shaped pattern.Basically, what is required is that these protrusions or indentationsonly need be arranged irregularly so as to suppress interference of thereflected light in the reflection electrode, thereby enabling to realizea bright preferable reflection characteristic not affected by thewavelength.

FIG. 3 and FIG. 4 are cross sectional views showing a reflective LCDapparatus according to Embodiment B2 of the present invention.Hereinafter, explanation will be given with reference to these figures.

In this embodiment, the insulation film below the reflection electrodeconsists of a convex/concave-shaped film and an inter-layer film whichare formed in separate steps. Firstly, a lower-layer film 70 is formed(FIG. 3[b]) and an upper-layer film 71 is formed (FIG. 3[c]). Next,photoresist patterning is performed to form a convex/concave pattern inthe upper-layer film 71. Thus, the upper-layer film 71 serves as aconvex/concave-shaped 72 and the lower-layer film 70 serves as aninter-layer film 73 (FIG. 4[d]). The other production steps areidentical to those in the aforementioned embodiment of FIG. 2.

The lower-layer film 70 and the upper-layer film 71 may be formed fromdifferent materials. For example, the upper layer film 71 may be madefrom an organic resin such as acrylic resin with which theconvex/concave shape can preferably be controlled while the lower-layerfilm 70 may be made from an inorganic insulation film such as a siliconnitride film having an excellent electric insulation, passivationcharacteristic, and process resistance. Moreover, the films to serve asthe convex/concave-shaped film 72 and the inter-layer film 73 may alsobe formed from other materials in various combination if they satisfythe aforementioned requirements.

It should be noted that although explanation has been given on a casethat a thin film transistor of the inverse stager structure is used asthe switching element in this embodiment, it is also possible to use athin film transistor or MIM diode of the forward stagger structure asthe switching element. Moreover, the glass substrate used as the lowersubstrate and the opposing substrate may be replaced by a plasticsubstrate, a ceramic substrate, a semiconductor substrate, and the like.Furthermore, it is also possible to use a combination of these differentsubstrates.

FIG. 5 shows a reflective LCD apparatus production method according toEmbodiment B3 of the present invention. Hereinafter, explanation will begiven with reference to this figure.

In this embodiment, protrusions formed are then subjected to a thermaltreatment to change the convex/concave shape so as to obtain a smoothconvex/concave structure under the reflective under the reflectionelectrode. The procedure to be performed up to the step FIG. 5[a] isidentical to the procedure for forming the thin film transistor shown inFIG. 2. Next, an insulation film 74 is formed with protrusions andindentations (FIG. 5[b]) and then subjected to a thermal treatment formelting, thereby changing it into an insulation film 74′ having a smoothconvex/concave structure (FIG. 5[c]). Here, by changing the baketemperature and the bake time to change the melting state of theprotrusions of the insulation film 74, it is possible to adjust thefinal convex/concave structure obtained. It should be noted that in thisembodiment the thermal treatment is used to obtain a smoothconvex/concave structure but it is also possible to expose the materialused for the convex/concave structure to a solvent having a melting orswelling characteristic so as to obtain a smooth convex/concavestructure.

After this, a contact hole 62 is formed (FIG. 5[d]) and a reflectionelectrode 63 is formed (FIG. 5[e]), thus completing production of thereflective TFT substrate. Thus the surface of the reflection electrode63 can have a smooth convex/concave shape, thereby enabling to obtain apreferable reflection optical characteristic. The reflective LCDapparatus using this TFR substrate can realize a bright display. In thisembodiment, in order to obtain a smooth convex/concave structure, athermal treatment is used for melting. However, other methods can alsobe used to obtain the same effect. For example, it is possible to use achemical for dissolving.

In the embodiments shown in FIG. 2 and FIG. 5, the insulation filmlocated under the reflection electrode is formed by one step using asingle material. That is, a single-layered film is formed as aninsulation film under the reflection electrode and this single-layeredfilm is patterned by the lift-off process. The insulation film is etchedfor selectively forming regions having a large film thickness andregions having a small film thickness, so as to be used for aconvex/concave structure. Thus, the convex/concave structure can beformed by a single layer film, which simplifies the productionprocedure, enabling to provide a reflective LCD apparatus as a lowercost.

In the aforementioned embodiments, the photolithography is used to formthe convex/concave structure by selectively forming regions having alarge film thickness and regions having a small film thickness of theinsulation film. However, it is also possible to use the screen printingmethod and adjust the film thickness of the print resin or to apply achemical solution to the surface of the insulation film to make thesurface rough to cause differences in the film thickness.

In the embodiments of FIG. 2 and FIG. 5, the insulation film under thereflection electrode is formed by a single step using a single material.However, as shown in the embodiment of FIG. 3 and FIG. 4, it is alsopossible to form an undercoat film and an upper film having protrusionsby different production steps. Alternatively, it is possible to form theconvex/concave structure using films formed from different materials.This can be used as the convex/concave structure of the insulation filmto form the reflection electrode, enabling to obtain a reflectionelectrode having a desired optical characteristic. In this case,although there is a disadvantage that the number of production steps isincreased, there is an advantage that it is possible to adjust thethickness of the undercoat film accurately.

FIG. 6 is a cross sectional view showing a reflective LCD apparatusaccording to Embodiment A2 of the present invention. Hereinafter,explanation will be given with reference to this figure.

In this embodiment, the insulation film 45 under the reflectionelectrode 45 is formed so as to cover the thin film transistor 44, thewiring 80, and the electrode 81. The reflection electrode 48 as thereflection plate and the pixel electrode electrically connected to thethin film transistor 44 by the contact portion 49 is electricallyisolated from the lower layer via the insulation film 45. That is, theinsulation film 45 has a function as a protection film. The insulationfilm 45 in this embodiment is in a direct contact with the thin filmtransistor 44 so as to be used as a passivation film of the thin filmtransistor 44. Between the insulation film 45 and the thin filmtransistor 44, it is possible to insert a silicon nitride film (SiN) ora silicon oxide film (SiO) conventionally used as a protection film ofthe thin film transistor 44.

FIG. 7 is a cross sectional view showing a reflective LCD apparatusaccording to Embodiment A3 of the present invention. Hereinafter,explanation will be given with reference to this figure.

In this embodiment, an insulation film 101 to be formed under thereflection electrode 48 may be formed using an organic resin or aninorganic resin if it has an insulation characteristic. Furthermore, theresin may have a transparency, coloring, and light-absorptioncharacteristics. Especially when the insulation film 101 has alight-absorption characteristic, the light 100 incident between adjacentreflection electrodes 48 can be completely absorbed by the insulationfilm 101, thereby preventing light introduction into the thin filmtransistor 44. This can prevent light off-leak of the thin filmtransistor 44 characteristic, thereby enabling to realize a reflectiveLCD apparatus having a preferable switching element characteristic.

Here, the insulation film 100 having the light-absorption characteristiccan be arranged at any position if it prevents the light from radiatingthe thin film transistor 44. Moreover, the insulation film 101 alsoserves as the insulation film having a smooth convex/concave structureunder the reflection electrode 48. This simplifies the productionprocess. When the insulation film 101 is made from “Black Resist” (tradename), “CFPR” (trade name), “BK-748S” (trade name), or “BK-430S” (tradename) which are produced by Tokyo Oyo-kagaku Kogyo Co., Ltd., it ispossible to form a preferable light absorbing layer and a preferableconvex/concave structure. Moreover, by using other Black resinmaterials, it is possible to obtain the similar effect. Furthermore, thelight absorption layer may be replaced by a film having a lightreflection characteristic such as a metal material or an insulationmaterial or an inorganic compound film not transmitting light at all.

FIG. 8 is a plan view of a mask pattern used in a reflective LCDapparatus according to Embodiment A4 of the present invention.

As has been described in the aforementioned embodiments, thecross-sectional configuration of the convex/concave structure of theinsulation film under the reflection electrode is selectively formedregions having a large film thickness and regions having a small filmthickness in the insulation film. This convex/concave structuredetermines the convex/concave structure of the reflection electrodesurface. This convex/concave structure of the insulation film is formedby using patterns irregularly arranged in a mask. FIG. 8 shows a maskpattern corresponding to one pixel used for formation of thisconvex/concave structure. It should be noted that reference numerals 110and 112 denote light transmitting regions.

In this embodiment, protrusion patterns are irregularly arranged. Eachof the protrusions has a size of about 2 to 20 micrometers and they arearranged at a pitch of about 2 to 40 micrometers. In FIG. 8[a],island-shaped protrusion patterns 111 are irregularly arranged, and inFIG. 8[b], line-shaped protrusion patterns 113 are irregularly arranged.Each of the masks enables to form a reflection electrode having apreferable reflection optical characteristic. Accordingly, thereflective LCD apparatus produced using these masks can have apreferable display characteristic.

It should be noted that in this embodiment the island-shaped patternshave an identical size and the line-shaped patterns have an identicalthickness. However, the present invention is not to be limited to suchpatterns. For example, the island-shaped patterns may have differentsizes and different shapes other than rectangular shape such aspolygonal shapes (such as triangular, pentagonal, hexagonal, heptagonalshapes), circular shapes, and elliptic shapes. Furthermore, acombination of different shapes can also exhibit the similar effect. Inthe case of the line-shaped patterns, it is possible to use linepatterns having various width values or curved lines. Moreover, it isalso possible to use a combination of the island-shaped patterns and theline-shaped patterns.

FIG. 9 is a plan view of a mask pattern used in a reflective LCDapparatus according to Embodiment A5 of the present invention.Hereinafter, explanation will be given with reference to this figure.

In this embodiment, the mask pattern has an inverse patterning of themask pattern of FIG. 8. That is, hole-shaped indentation patterns 115 orgroove-shaped indentation patterns 117 are irregularly arranged. Byusing such ask patterns, it has been possible to obtain a high-luminancereflection electrode. Here, the indentation patterns have a size ofabout 2 to 20 micrometers and are arranged at a pitch of about 2 to 40micrometers. It should be noted that reference numerals 114 and 116 areregions not transmitting light.

In this embodiment also, the hole-shaped patterns having an identicalsize or groove-shaped patterns having an identical width are used.However, the present invention is not to be limited to these patterns.For example, the hole-shaped patterns may have different sizes andshapes other than the rectangular shape such as a polygonal shape(triangular, pentagonal, hexagonal, heptagonal shapes), circular shape,or elliptic shape. Furthermore, a combination of various shapes can alsoexhibit the similar effect. Furthermore, in the case of thegroove-shaped pattern, it is possible to use line patterns havingdifferent width values or curved patterns. These patterns may becompletely different from one another. Moreover, it is possible to use acombination of the hole-shaped patterns and the line-shaped patterns.

FIG. 10 explains a reflective LCD apparatus according to Embodiment A6of the present invention. Hereinafter, explanation will be given withreference to this figure.

In this embodiment, the convex/concave pattern need be irregular atleast within a pixel of the reflective LCD apparatus. For example, thepattern may be irregular within a three-pixel region or four-pixelregion of the RGB or RGGB. Moreover, the pattern may be irregular overmore than four pixels. Thus, the pattern is repeated to form theconvex/concave structure in the reflection electrode region over theentire panel display surface. In this case, it is possible to obtain areflection plate having the similar luminance as in the case when theentire surface of the reflection plate panel is formed by a completelyirregular pattern.

FIG. 10[a] shows a display region formed with one irregular pattern overthe entire display surface. FIG. 10[b] shows a display region formed byrepetition of an irregular pattern within one pixel. FIG. 10[c] shows adisplay region formed by repetition of an irregular pattern within morethan one pixel. It is preferable to repeat an irregular pattern withinmore than one pixel to form the convex/concave structure over the entirereflection electrode region. It should be noted that the presentembodiment has been explained using a island-shaped pattern. However,the present invention is not to be limited to this. As shown in FIG. 8and FIG. 9, the same effect can be realized by using the line-shapedpattern, the hole-shaped pattern, and the groove-shaped pattern.

FIG. 12 is a cross sectional view showing a reflective LCD apparatusproduction method according to Embodiment B4 of the present inventionand FIG. 11 shows a comparative example. Hereinafter, explanation willbe given with reference to these figures.

This embodiment is identical to the embodiment of FIG. 2 except for thatthe insulation film under the reflection electrode is formed from amaterial having photosensitivity. FIG. 11 shows a comparative example inwhich the convex/concave pattern is formed in the insulation film 133using photoresist. FIG. 12 shows the present embodiment B4. In thisembodiment, the insulation film under the reflection electrode consistsof an upper protrusion 130 and a lower layer film 131 which are bothmade from a photosensitive resin 132. In this case, the photosensitiveresin 132 is applied and then exposed and developed to simultaneouslyform the upper protrusion 130 and the lower layer film 131.

This embodiment using a photosensitive resin eliminates need to performthe step of mask pattern 135 by the photoreist layer 134: FIGS. 11[B1],[c 1], and [d 1]. That is, the patterning can be performed by directlyexposing and developing the photosensitive resin and it is possible tosimplify the resit application and peel-off step. Thus, the number ofproduction steps cn be reduced as compared to the Comparative Example ofFIG. 11. As a result, it is possible to provide the reflective LCDapparatus as a lower cost.

It should be noted that the photosensitive resin used in this embodimentmay be an organic resin such as acrylic resin and polyimide resin, or aninorganic resin. Moreover, as has been described above, the insulationfilm under the reflectdion electrode may consist of the upper protrusionportion and the lower layer film made from different photosensitiveresins. Furthermore, it is possible to use a photosensitive resin onlyfor the upper protrusion portion or the lower layer film. Moreover, thelower substrate or the opposing substrate used in this embodiment may beformed from a material other than the glass substrate. Moreover, thephotosensitive resin used in this embodiment need not be transparent andmay be black capable of absorbing light. For a semi-transparent LCDapparatus, a transparent photosensitive material can be used, and for areflective LCD apparatus, a black photosensitive material can be used(as shown in Embodiment A7 below) FIG. 13 is a cross sectional viewshowing a reflective LCD apparatus according to A7 of the presentinvention. Hereinafter, explanation will be given with reference to thisfigure.

FIG. 13[a] shows a reflective LCD apparatus using a black photosensitivematerial for an insulation film 101 a. FIG. 13[b] shows asemi-transparent LCD apparatus, i.e., a reflective LCD apparatus alsoserving as a transparent type LCD apparatus, using a transparentphotosensitive material for an insulation film 101 b. In FIG. 13[b], byreducing the film thickness of the reflection electrode 48′, the lightof the back light 140 can pass through. It should be noted that thesemi-transparent LCD apparatus is not to be limited to theaforementioned configuration. For example, it is possible to form atleast one opening in the reflection electrode within each pixel of acertain region on the screen, so that the back light 141 can passthrough that region.

FIG. 14 and FIG. 15 show a reflective LCD apparatus production methodaccording to Embodiment B5 of the present invention in cross sectionalviews. Hereinafter, explanation will be given with reference to thesefigures.

In this embodiment, a thin film transistor of inverse stagger structureis used as a switching element. The TFT substrate production procedurein this embodiment includes: [a] formation of an electrode material, [b]formation of a gate electrode 150, [c] formation of a gate insulationfilm 151, a semiconductor layer 152, and a doping layer 153, [d]formation of an electrode material, [e] formation of an island, [f]formation of a source electrode 155 and a drain electrode 156, [g]formation of an insulation film 157, [h] formation of a convex/concavestructure 158 in the upper layer of the insulation film, [i] formationof a contact hole, and [j] formation of a reflection electrode 160.

Furthermore, step [h] includes (1) formation of resist 163 on theinsulation film 157, (2) formation of the convex/concave pattern 164,(3) formation of a convex/concave structure 158 on the upper layer ofthe insulation film 157, and (4) peeling off of the resist. Here, theheight of protrusions X in the convex/concave structure and the filmthickness Y of the lower layer can be adjusted by controlling theetching amount of the upper layer of the insulation film 157.Accordingly, the height X can be determined according to desiredreflection plate optical characteristic while the lower layer filmthickness Y can be determined according to the coverage and insulationcharacteristic for the switching element and wiring in the undercoatlayer.

It should be noted that while the present embodiment has been explainedfor the case when using the thin film transistor of the inverse staggerconfiguration as the switching element, it is also possible to use athin film transistor of forward stagger configuration or MIM diode asthe switching element. Moreover, the thin film transistor of the inversestagger configuration is not to be limited to the one explained in thisembodiment but may have a configuration other than this. Moreover, theglass substrate used for the lower substrate and the opposing substratemay be replaced by a plastic substrate, a ceramic substrate asemiconductor substrate, or the like. Furthermore, in the presentembodiment, the step (3) for forming a convex/concave structure on thesurface of the insulation film may be performed as formation of aplurality of films by a plurality of steps.

FIG. 16 and FIG. 17 shows a reflective LCD apparatus production methodaccording Embodiment B6 of the present invention in cross sectionalviews. Hereinafter, explanation will be given with reference to thesefigures.

The present embodiment is identical to the production procedure of FIG.14 and FIG. 15 except for the formation of an insulation film having aconvex/concave structure on the surface. That is, after the steps FIG.14[a] to [f] including the formation of the switching element, theinsulation film having the convex/concave structure according to thepresent embodiment is formed by (1) formation of an insulation layer 161for inter-layer film, (2) formation of an insulation layer 162 forforming protrusions and indentations, (3) formation of theconvex/concave pattern 164 using the resist 163, (4) formation of theconvex/concave structure 165, and (5) peeling off of the resist.

Thus, the convex/concave layer 166 and the lower layer film 167 of theinsulation layer formed under the reflection electrode can be formed byseparate steps. For this, the convex/concave layer of the upper layercan be formed by using acrylic resin capable of easily controlling theconvex/concave structure for the convex/concave layer of the upper layerwhile the lower layer can be formed by using silicon nitride havingexcellent passivation or electric insulation characteristic with respectto the undercoat. Thus, it is possible to provide a switching elementsubstrate having a preferable optical characteristic as well aspreferable element characteristic. This enables to realize a reflectiveLCD apparatus exhibiting a high performance and high quality display.

It should be noted that the convex/concave layer and the lower layerfilm used in this embodiment are not to be limited to theaforementioned. It is possible to use an organic insulation film such aspolyimide and an inorganic insulation film such as silicon oxide film orto use a single material for both of the upper layer and the lowerlayer.

FIG. 18 and FIG. 19 are cross sectional views showing a reflective LCDapparatus production method according to Embodiment B7 of the presentinvention. Hereinafter, explanation will be given with reference tothese figures.

This embodiment is identical to the embodiment of FIG. 14 and FIG. 15except for that the insulation film 157 under the reflection electrode160 is formed from a material having photosensitivity.

According to this embodiment, patterning can be performed by directlyexposing and developing the photosensitive resin, which simplifies theresist application and peel-off steps, significantly reducing the numberof the production steps shown in FIG. 14 and FIG. 15. This enables toprovide a reflective LCD apparatus at a low cost.

FIG. 20 and FIG. 21 are cross sectional views showing a reflective LCDapparatus production method according to Embodiment B8 of the presentinvention. Hereinafter, explanation will be given with reference tothese figures.

This embodiment is identical to the embodiment shown in FIG. 18 and FIG.19 except for that the contact hole formation in the insulation filmunder the reflection electrode is performed simultaneously with theprotrusion/indentation formation. In this embodiment, the TFT substrateis produced by the following steps: [a] formation of the electrodematerial, [b] formation of the gate electrode, [c] formation of the gateinsulation film, the semiconductor layer, and the doping layer, [d]formation of the electrode material, [e] formation of the island, and[f] formation of the source electrode and the drain electrode, which arefollowed by [g] formation of the photosensitive insulation layer 170,[h] exposure to the photosensitive insulation layer (the contact region171 and the convex/concave region 172), [i] simultaneous formation ofthe contact to the photosensitive insulation layer andprotrusions/indentations and melting of the protrusion and indentationsurfaces by thermal treatment, and [j] formation of the reflectionelectrode 173.

In step [h] of this embodiment, a pattern of the contact formationregion and a pattern of the protrusion/indentation formation region aresimultaneously exposed in a single exposure step. After this, in thedevelopment/etching step, the etching is performed so that theindentations have a depth of X and the contact formation portions have adepth of Z.

In this step [h], the exposure energy amount need adjusted so that moreenergy is applied to the contact portion 174 than to the convex/concavepattern portion 175 and the lower layer portion of the photosensitiveinsulation layer 170 has a desired film thickness Y. The exposure amountadjustment may be made, for example, by using a convex/concave patternformation mask and a contact pattern formation mask and performing dualexposure so that the exposure amount differs in respective patterns.Alternatively, it is possible to use a single mask in which a maskmaterial is adjusted to obtain different light transmission values forthe concave/convex pattern portion and the contact pattern portion.Thus, by providing different exposure energies for the respectivepatterns in the exposure step, it is possible to realize patternformations having different etching amounts within a single substrateunder a single development condition. In this embodiment, theconvex/concave surface is converted into a smooth convex/concave curveby performing a thermal treatment to the insulation film.

According to this embodiment, patterning can be performed by directlyexposing and developing the photosensitive resin and it is possible tosimultaneously perform the protrusions/indentations formation step andthe contact formation step with a single exposure anddevelopment/etching. This further reduces the number of production stepsas compared to the embodiment shown in FIG. 18 and FIG. 19, enabling toprovide a reflective LCD apparatus at a low cost.

Moreover, in this embodiment, a photosensitive material is used forformation of the convex/concave insulation layer. When a resist processis performed, the same configuration can be obtained using anon-photosensitive material. Although this increases the number ofsteps, the number is still smaller as compared to the conventionalreflective LCD apparatus production method.

EXAMPLES Example 1

FIG. 22 and FIG. 23 show production steps for producing a reflective LCDapparatus in this example. As a switching element, a thin filmtransistor of forward stagger structure was used.

The production was performed by following production steps on a glasssubstrate.

-   -   [a] formation of an ITO film with 50 nm thickness by sputtering    -   [b] formation of a source 200 and a drain electrode 201 (using        1st photoresist)    -   [c] use of plasma CVD to form a doping layer 202 with 100 nm        thickness, a semiconductor layer 203 with 100 nm thickness, and        a gate insulation film 204 with 400 nm thickness    -   [d] formation of a Cr layer 205 with 50 nm thickness by        sputtering    -   [e] formation of a gate electrode and an island 206 of the TFT        element portion (using 2nd photoresisit)    -   [f] formation of an organic insulation film 207 (3 micrometers)    -   [g] formation of a convex/concave pattern 208 on the upper layer        of the organic insulation film (using 3rd photoresist)    -   [h] formation of a contact 209 (using 4th photoresist)    -   [i] formation of an aluminum film with 300 nm thickness by        sputtering    -   [j] formation of a reflection pixel electrode plate 210 (using        5th photoresist)

It should be noted that in the aforementioned step [c], a combination ofa silicon oxide film and a silicon nitride film was used for the gateinsulation film, an amorphous silicon film was used for thesemiconductor layer, and an n-type amorphous silicon film was used forthe doping layer. The plasma CVD condition for them was set as follows.For the silicon oxide film, silane and oxygen were used as reactiongases which were supplied at a ratio (silane/oxygen) of 0.1 to 0.5; andthe film formation was performed at a temperature of 200 to 300 degreesC. under a pressure of 133 Pa with a plasma power of 200 W. For thesilicon oxide film, silane and ammonium were used as reaction gasseswhich were supplied a ratio (silane/ammonium) of 0.1 to 0.8; and thefilm formation was performed at a temperature of 250 degrees C. underpressure of 133 Pa with a plasma power of 200 W. For the amorphoussilicon, silane and hydrogen were used as reaction gases which weresupplied at a ratio (silane/hydrogen) of 0.25 to 2; and the filmformation was performed at a temperature of 200 to 250 degrees C. undera pressure of 133 Pa with a plasma power of 50 W. For the n-typeamorphous silicon film, silane and phosphoine were used as reactiongasses which were supplied at a ratio (silane/phosphine) of 1 to 2, andthe film formation was performed at a temperature of 200 to 250 degreesC. under a pressure of 133 Pa with a plasma power of 50 W.

Moreover, in the aforementioned step [e] for forming an island of theTFT element portion, wet etching was used for the Cr layer and dryetching was used for the silicon oxide film, the silicon nitride film,and the amorphous silicon layer. The etching of the Cr layer wasperformed by using an aqueous solution mixture of perhydrochloric acidand serium II nitrate ammonium. Moreover, the etching of the nitratefilm and the silicon oxide film was performed by using as the etchinggas fluorine tetracholoride and oxygen under a reaction pressure of0.665 to 39.9 Pa with a plasma power of 100 to 300 W. Moreover, theetching of the amorphous silicon layer was performed by using chlorineand hydrogen gases under a reaction pressure of 0.665 to 39.9 Pa with aplasma power of 50 to 200 W. Moreover, the photolithography step wasperformed by using the conventional resist process.

In this example, ITO was used for the source and the drain electrode,but it is also possible to use a material other than this such as Ti, W,Mo, Ta, Cu, Al, Ag, ZnO, SnO to form a single-layered film or amulti-layered film using a combination of these materials. The gateelectrode can also be formed by using other than Cr such as Ti, W, Mo,Ta, Cu, Al, Ag, and the like to form a single-layered film ormulti-layered film using a combination of these materials.

In this example, the protrusions/indentations under the reflectionelectrode are formed in the aforementioned steps [f] and [g]. That is,on the insulation film formed in step [f], a resist film of 2micrometers is formed and exposed and developed to form a convex/concaveresist pattern. The insulation film was etched to obtain a depth of 1micrometer and the resist was peeled off to form a convex/concavestructure in the upper layer of the insulation layer.

In the aforementioned step [f] for forming the organic insulation film,polyimide (“RN-812” (trade name) produced by Nissan Kagaku Kogyo Co.,Ltd.) was used. The polyimide was applied at spin rotation speed of 1200rpm. The pre-bake was performed at temperature of 90 degrees C. for 10minutes, and the post-bake was performed at temperature of 250 degreesfor 1 hour. On the other hand, in the case of the resist used for thepattern formation, the spin rotation speed was set to 1000 rpm, thepreparatory baking was set to 90 degrees C. for 5 minutes. After this,pattern formation was performed by exposure and development and apost-bake was performed at 90 degrees C. for 30 minutes. The dry etchingof the polyimide film using the resist pattern as a mask layer wasperformed by using as a etching gas a mixture of fluorine tetrachlorideand oxygen which were supplied at a rate (fluorine tetrachloride/oxygen)of 0.5 to 1.5 under a reaction pressure of 0.665 to 39.9 Pa with aplasma power of 100 to 300 W. It should be noted that thephotolithography was performed using a conventional resist process.

Moreover, in this example, the insulation layer formed by a single stepis also used for the convex/concave insulation layer located between thereflection plate and the TFT element. As another example, aftercompletion of the TFT formation in step [e], a first insulation film (2micrometers) using an organic resin, a second insulation film was formed(1 micrometer) using an organic resin, and a resist process and anetching process were performed to form a convex/concave structure in thesecond organic resin. Thus, it was also possible to form a desiredconvex/concave insulation layer. The basic production process isidentical to the one in the aforementioned example.

Moreover, while the first insulation film and the second insulation filmwere formed by using a single organic resin material, it was alsopossible to form the convex/concave insulation layer by using differentmaterials, including a combination of an inorganic resin and an organicresin such as acrylic resin and polyimide resin; silicon nitride filmand acrylic resin; and silicon oxide film and polyimide resin.

In Example 1, an aluminum metal having a high reflection efficiency andcapability for the TFT process was formed and patterned to form thepixel electrode also serving as the reflection plate. Here, the aluminumwas subjected to wet etching using an etching liquid consisting ofphosphoric acid, acetic acid, and nitric acid heated to 60 degrees C.

In this example, during the protrusions/indentations formation step, thepatterning for forming the protrusions/indentations is performed whilethe switching element is covered by the insulation layer. Accordingly,the switching element is not exposed directly to the etching process.Thus, there is no danger of damaging the switching elementcharacteristic or causing a problem such as instability and it ispossible to obtain a reflective LCD having a high performance.

It should be noted that the maximum height of protrusions was set toabout 1 micrometer and the convex/concave structure was set to a randomshape. After this, the aforementioned TFT substrate was attached to theopposing substrate having the transparent electrode made from ITO insuch a manner that their film surfaces oppose to each other. It shouldbe noted that the TFT substrate and the opposing substrate weresubjected to an orientation treatment and they are attached to eachother via spacers such as plastic particles by applying an epoxy-basedadhesive to the peripheral portion of the panel. After that, a liquidcrystal was introduced to form a liquid crystal layer, thus completingthe reflective LCD apparatus.

FIG. 24 is a cross sectional view of the reflective LCD apparatusobtained in Example 1. In FIG. 24, the LCD apparatus includes anopposing substrate 212, an upper glass substrate 213, a color filter214, an ITO (indium tin oxide), a liquid crystal 218, a reflection plate219, an organic insulation film 220, and a glass substrate 221.Reference numeral 216 denotes an incident light and 217, a reflectedlight.

This reflective LCD apparatus includes a reflection pixel electrodehaving uniform reflection capability preferably scattering light.Accordingly, it is possible to realize a monochromatic reflective panelhaving a white display of luminance higher than a newspaper at a lowcost. Moreover, when an RPG color filter is arranged on the opposingsubstrate, it is possible to realize a bright color reflective panel ata low cost.

It should be noted that the height of protrusions of the convex/concavestructure is not to be limited to the aforementioned value. The heightof protrusions may be varied in a wide range and by using thisconvex/concave structure, it is possible to provide a reflective LCDapparatus in which directivity of the reflection plate performance issignificantly changed.

Example 2

FIG. 25 and FIG. 26 show production steps for producing a reflective LCDapparatus used in Example 2. For the switching element in thisreflective LCD apparatus, a thin film transistor of inverse staggerconfiguration was used.

The production was performed on the glass substrate 230 throughfollowing steps.

-   -   [a] formation of Cr film of 50 nm thickness by sputtering    -   [b] formation of a gate electrode 231 (1st photoresist)    -   [c] formation of a gate insulation film 232 of 400 nm thickness,        a semiconductor layer 233 of 100 nm thickness, and a doping        layer 234 of 100 nm thickness by using the CVD method    -   [d] formation of an island 235 (2nd photoresist)    -   [e] formation of a Cr layer and an ITO layer by sputtering    -   [f] formation of a source electrode 236 and a drain electrode        237 (3rd photoresist)    -   [g] formation of an organic insulation film 238 (3 micrometers)    -   [h] formation of a convex/concave pattern 239 in the upper layer        portion of the organic insulation film (4th photoresist)    -   [i] formation of a contacdt 241 (5th photoresist)    -   [j] formation of an aluminum 242 with 300 nm thickness by        sputtering    -   [k] formation of a reflection pixel electrode plate 243 (6th        photoresist)    -   [l] taking out of a gate line (7th photoresist)

In this example, the protrusions/indentations 240 under the reflectionplate are formed in the aforementioned step [g]. The formationconditions were set identically as in Example 1. In this example, sincethe transistor configuration uses the inverse stagger configuration, thenumber of steps is increased as compared to Example 1.

It should be noted that the ratio of hole area in the reflection pixelelectrode plate in this example was set to 86%. The TFT substrate wasattached to the opposing substrate having the transparent electrode madefrom ITO in such a manner that their film surfaces oppose to each other.The TFT substrate and the opposing substrate were subjected to anorientation treatment and attached to each other via a spacer such asplastic particles by applying an epoxy-based adhesive to a panelperipheral portion. After this, GH-type liquid crystal was introduced toform a liquid crystal layer, thus completing the reflective LCDapparatus.

FIG. 27 is a cross sectional view of the reflective LCD apparatusproduced in this example. The reflective LCD apparatus includes a resistconvex/concave pattern 239, a contact 241, a reflection plate 243, anopposing substrate 250, a glass substrate 251, a color filter 252, atransparent electrode 253, and a guest-host liquid crystal 254. Areference numeral 15 denotes an incident light and 16, a reflectedlight.

In the reflective LCD apparatus of this example, like in Example 1, noprocess damage is given to the switching element, enabling to obtain apreferable element characteristic and a desired convex/concavereflection plate structure. As a result, the color reflective panelproduced in this example had a bright high-quality display.

Example 3

In this example, the convex/concave surface under the reflectiveelectrode has a smooth convex/concave configuration. FIG. 28 and FIG. 29are cross sectional views of the reflective LCD apparatus produced inthis example.

This example is identical to Example 1 and Example 2 except for that anadditional step is performed for converting the protrusions/indentationsunder the reflection electrode into a smooth shape. More specifically, astep for applying a thermal treatment is added after the step [i] inExample 1 and after the step [h] in Example 2. Accordingly, FIG. 28 isidentical to FIG. 25.

In this example, the thermal treatment after the formation of theprotrusions/indentations was performed in an oven under a nitrogenatmosphere at 260 degrees C. for 1 hour. By this thermal treatment, theinclination angle of the protrusions/indentations was changed from arange 60 to 80 degrees to a range 10 to 40 degrees. That is, theconvex/concave shape was changed from a rectangular shape to a smoothsinusoidal curve surface 261. It should be noted that in the reflectiveLCD apparatus of this example, the average value of theprotrusions/indentations inclination angle was set to about 8 degrees.Moreover, the protrusion/indentation inclination angle can be controlledby changing the bake temperature in the aforementioned thermal treatmentstep.

Moreover, in this example, the height of the protrusions was set to 1micrometer like in Examples 1 and 2. It should be noted that by makingthe protrusion height higher, it is possible to obtain a reflectionplate having an optical characteristic showing a higher scatteringdegree. This reduces the dependency of luminance on the field of viewand enables to provide a reflective LCD apparatus that can easily beviewed. This advantage is especially great when the reflective LCDapparatus has a large-size screen.

Moreover, by reducing the height of the protrusions, it is possible toobtain a strong directivity as the optical characteristic of thereflection plate. In this case, by applying the present invention to areflective LCD apparatus for a portable information apparatus having acomparatively small screen size, it is possible to realize a brighterdisplay characteristic. Thus, it is possible to control theconvex/concave structure according to the application or the paneldisplay area.

Moreover, the insulation layer in this example is located between thereflection plate located above and the switching element located below,thereby serving as a protection film for the switching element.

Example 4

In this example, the insulation layer under the reflection plate is madeby an organic insulation film having photosensitivity. FIG. 30 and FIG.31 are cross sectional views of a reflective LCD apparatus produced inthis example.

The production procedure for producing a reflective LCD apparatus inthis example is identical to Example 1 or 2 except for that aphotosensitive resin (photosensitive acrylic resin in this example) isused for the insulation layer under the reflection plate. Morespecifically, a photosensitive film 270 is used for the insulation layerformed in step [f] of Example 1 and step [g] of Example 2.

Thus, the convex/concave structure is formed by a step for forming thephotosensitive film, a step of direct exposure to the photosensitivefilm, an etching-development step, and a melt step by thermal treatment.Accordingly, as compared to the convex/concave structure formationperformed in Examples 1, 2, and 3, there is no need of the resistapplication step, the resist development step, and the resist peel-offstep. Thus, the production procedure is simplified.

In this example, a photosensitive acrylic resin is used as thephotosensitive material. However, the photosensitive material is not tobe limited to this. It is also possible to use a photosensitive organicresin or a photosensitive inorganic film to obtain the same effect. Itshould be noted that the similar convex/concave insulation layer wasobtained by using as the photosensitive material, “OFPR800” (trade name)produced by Tokyo Oyo-kagaku Kogyo Co., Ltd., “LC100” (trade name)produced by Sipray Co., Ltd., “Optomer series” (trade name) produced byNihon Synthetic Rubber Co., Ltd., and “Photosensitive Polyimide” (tradename) produced by Nihon Kagaku Kogyo Co., Ltd.

Example 5

FIG. 32 and FIG. 33 show production steps for producing a reflective LCDapparatus used in this example. As the switching element, a thin filmtransistor of inverse stagger structure was used.

The production is performed on the glass substrate 230 as follows.

-   -   [a] formation of a Cr film of 50 nm thickness by sputtering    -   [b] formation of a gate electrode 231 (1st photoresist)    -   [c] formation of a gate insulation film 234 of 400 nm thickness,        a semiconductor layer 233 of 100 nm thickness, and a doping        layer 234 of 100 nm thickness by the plasma CVD    -   [d] formation of an island 235 (2nd photoresist)    -   [e] formation of a Cr layer of 50 nm thickness and an ITO layer        of 50 nm thickness by sputtering    -   [f] formation of a source electrode 237, a drain electrode 236        and an electrode 130 for formation of the convex/concave        structure (3rd photoresist)    -   [g] formation of a photosensitive acrylic resin 270 (3        micrometers)    -   [h] exposure of the convex/concave pattern and the contact        pattern onto the phtoosensitive acrylic resin (4th photoresist)    -   [i] simultaneous formation of protrusions/indentations 239 and        the contact 241 by development-etching    -   [j] formation of an aluminum film 242 of 300 nm thickness by        sputtering    -   [k] formation of the reflection pixel electrode plate 243 (5th        photoresist)    -   [l] taking out of a gate line terminal (6th photoresist)

After this, the opposing substrate was placed on, thus completing thereflective LCD apparatus. The reflective LCD apparatus realized a brighthigh-quality color display.

Example 5 is identical to Example 3 except for that in step [h] theconvex/concave structure and the contact are simultaneously formed. Step[h] of Example 5 realizes step [i] in which the insulation film having afilm thickness of 3 micrometers are removed completely in the contactregion while a lower film of 2 micrometers is left in the convex/concaveregion.

More specifically, Example 5 uses a single mask having a contact pattern280 and a convex/concave pattern 281. The mask material 282 iscontrolled in such a manner that more light pass through the contactpattern region than in the convex/concave pattern. Thus, in the exposedphotosensitive acrylic resin 283, different radiation energies areapplied to the respective patterns. Accordingly, with the samedevelopment time, it is possible to simultaneously obtain differentetching amounts, i.e., a region having a desired film thickness and aregion having no film.

In this example, the light transmission ratio was controlled to be 3:1in the contact pattern region and in the convex/concave pattern region.In the development step, “NMD-3” (trade name, produced by TokyoOyo-kagaku Kogyo Co., Ltd.) was used and the development time was set to90 seconds. As a result, the film was completely removed in the contactregion and a lower layer film of 2 micrometers was left in theconvex/concave region.

In this example using a photosensitive material for the insulation filmand simultaneously forming the convex/concave pattern and the contactpattern, it is possible to reduce the production steps of the TFTsubstrate of the reflective LCD apparatus. Moreover, the application ofphotoresist is also reduced from 8 times to 6 times during theproduction of the TFT substrate. This enables to provide a reflectiveLCD apparatus at a reduced cost.

In this example, the exposure amount was controlled by controlling thetransmission amount of the mask material in the mask for simultaneouslyforming the convex/concave pattern and the contact pattern. It is alsopossible to use a convex/concave pattern mask and a contact pattern maskand perform exposure twice. In this case, it is necessary to set theexposure amount for the contact pattern greater than the exposure amountfor the convex/concave pattern.

Example 6

FIG. 35 is a cross sectional view of a reflective LCD apparatus used inthis example. The reflective LCD apparatus includes an opposingsubstrate 290, a concave/convex reflection plate 291, a convex/concavelayer 292, a pixel electrode 293, a signal line 294, a liquid crystallayer 295, an insulation layer 296, and an MIM element 297.

The switching element is an MIM diode element having a metal-insulationfilm-metal structure. In this case also, it was possible to obtain apreferable display performance in the same way when a thin filmtransistor is used as the switching element.

It should be noted that in the aforementioned figures, like componentsare denoted by like reference symbols and their explanations areomitted.

According to the reflective LCD apparatus and production method thereofaccording to the present invention, the insulation film having aconvex/concave structure under the reflection electrode protects theswitching element during a production; and the irregular arrangement ofregions having different film thickness values enables to suppressinterference of a reflected light from the reflection electrode, therebyenabling to prevent deterioration of characteristic of the switchingelement during the production. Moreover, since no other film is requiredfor the convex/concave structure, it is possible to reduce the number ofthe production steps.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristic thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

The entire disclosure of Japanese Patent Application No. 2000-006423(Filed on Jan. 14^(th), 2000) including specification, claims, drawingsand summary are incorporated herein by reference in its entirety.

1-15. (canceled).
 16. An LCD apparatus production method comprising thesteps of: among a pair of a first substrate and a second substrate, eachof which is transparent and is separately arranged so as to have apredetermined distance between each other, forming a transparentelectrode on the first substrate; forming a switching element on thesecond substrate; on the second substrate, forming an insulation film onan upper part of the switching element in a continuous face shape so asto protect the switching element by overlaying the same; on theinsulation film where the switching element is; protected, forming aconvex/concave structure on a surface facing the first substrate;forming a reflection electrode on the insulation film and then providingon a surface, facing the first substrate, of the reflection electrode ashape in which the convex/concave structure of the insulation film isreflected; and filling a liquid crystal layer in a space between thetransparent electrode of the first substrate and the reflectionelectrode of the second substrate.
 17. The method of producing the LCDapparatus as claimed in claim 16, wherein the insulation film islaminated as a single layer structure and the convex/concave structureis formed as a part of the surface, facing the first substrate, of theinsulation film.
 18. The method of producing the LCD apparatus asclaimed in claim 17, wherein a protrusion of the convex/concavestructure is formed as a continuous smooth shape.
 19. The method ofproducing the LCD apparatus as claimed in claim 17, wherein a pluralityof protrusions of the convex/concave structure and a plurality ofindentations indented downward from the protrusions are formed andarranged irregularly by using a mask pattern.
 20. The method ofproducing the LCD apparatus as claimed in claim 19, wherein theprotrusions are formed and arranged by using the mask pattern having anisland-shaped or line-shaped pattern.
 21. The method of producing theLCD apparatus as claimed in claim 19, wherein the indentations areformed and arranged ‘by using the mask pattern having a hole-shaped orline-shaped pattern.
 22. The method of producing the LCD apparatus asclaimed in claim 19, wherein the protrusions of the convex/concavestructure are formed and arranged irregularly using the mask patternhaving the island-shaped or, line-shaped pattern, based on one pixel ormore than one pixels as a unit.
 23. The method of producing the LCDapparatus as claimed in claim 19, wherein the indentations of the convexconcave structure are formed and arranged irregularly using the maskpattern having the hole-shaped or line-shaped pattern, based on onepixel or more than one pixels as a unit.
 24. The method of producing theLCD apparatus as claimed in claim 16, wherein the insulation film islaminated as a single layer structure and the convex/concave structureis formed on the surface, facing the first substrate, of the insulationfilm by using a separate insulation film.
 25. The method of producingthe LCD apparatus as claimed in claim 24, wherein a protrusion of theconvex/concave structure is formed as a continuous smooth shape.
 26. Themethod of producing the LCD apparatus as claimed in claim 25, wherein aplurality of protrusions of the convex/concave structure and a pluralityof indentations indented downward from the protrusions are formed andarranged irregularly by using a mask pattern.
 27. The method ofproducing the LCD apparatus as claimed in claim 24, wherein theprotrusions are formed and arranged by using the mask pattern having anisland-shaped or line-shaped pattern.
 28. The method of producing theLCD apparatus as claimed in claim 24, wherein the indentations areformed and arranged by using the mask pattern having a hole-shaped orline-shaped pattern.
 29. The method of producing the LCD apparatus asclaimed in claim 24, wherein the protrusions of the convex/concavestructure are formed and arranged irregularly using the mask patternhaving the island-shaped or line-shaped pattern, based on one pixel ormore than one pixels as a unit.
 30. The method of producing the LCDapparatus as claimed in claim 24, wherein the indentations of theconvex/concave structure are formed and arranged irregularly using themask pattern hawing the hole-shaped or line-shaped pattern, based on onepixel or more than one pixels as a unit.
 31. The method of producing LCDapparatus as claimed in claim 16, wherein the insulation film is formedof a transparent photosensitive material where a back light is able topass through.